Mark,
 
I agree with you regarding the desirable symmetry of peers, and the
'global' owner you suggest. Anyway, it seems that things aren't as
bad/sensitive as I thought. Harold told me that obviously:
       'if there is a path to the server for for mail,
   then there is a path to the server for the delete command'.
 
(but my doubt was that although mail can be distributed
through master-slave lists, may be some 'sensitive' commands are
not accepted from those servers whose equivalent list is non-peered).
 
Now, to avoid as much as possible the difficulties mentioned by Richard,
I insist on our willingness to get back the subscribers that were once
hosted in our server. Harri Salminen helped us a with a couple of lists,
but we would like that some other European postmasters were able to
EXPLODE their lists (and MOVE-ing the necessary subscribers or allowing
us -put the right 'Owner', please- to do it).
 
Best regards,  Miguel.